Pressure switch



Oct. 31, 1967 E. w. ERIKSON PRESSURE SWITCH 2 Sheets-Sheet 1 Filed Nov. 26, 1965 E. w. ERIKSON 3,350,523

PRESSURE SWITCH Oct. 31, 1967 Filed Nov. 26, 1965 2 Sheets-Sheet 2 United States Patent Ofiice 3,350,523 Patented Oct. 31, 1967 3,350,523 PRESSURE SWITCH Evans W. Erikson, Rockford, Ill., assignor to Snndstrand Corporation, a corporation of Illinois Filed Nov. 26, 1965, Ser. No. 509,710 16 Claims. (Cl. 200-82) ABSTRACT OF THE DISCLOSIRE This invention relates to pressure switches and, more particularly, to a hydraulic pressure sensitive switch for indicating a pressure condition above or below a predetermined value.

Pressure sensitive switches are craft charge pressure for certain hydraulic controls is at an acceptably high level and, also, to indicate that the drive output speed is in an acceptable range so that the drive supplies the desired power to the shaft of a synchronous generator coupled to the drive which provides the electric power supply for the aircraft. In the past, switches used for this purpose have consisted of a switch mechanism circuit making and breaking contacts arranged in bistable fashion and a hydraulically lived and unreliable in some applications because of the the contacts, ambient vibration, and because the temperature and pressure fluctuations have resulted in a relatively poor contact life.

In accordance with the present invention, a bistable pressure sensitive switch is provided which obviates the disadvantages described above inherent in prior known pressure sensing switching devices. The present switch consists basically of a variable inductance device with mean for varying the impedance thereof from a relatively low value to a relatively high value It is, therefore, a primary object of the invention to provide a new and improved pressure sensitive switch of Another object of the present invention is to provide a new and improved pressure sensitive switch having a variable inductance device adapted for bistable operation with means for selectively establishing a low impedance condition and a high impedance condition.

A further object of the present invention is to provide a new and improved pressure sensitive switch of the type described above in which means are provided for collecting foreign matter in the hydraulic fluid to prevent the accumulation of foreign particles in the air gap of the variable inductance device. Preferably, this particle collector takes the form of a permanent magnet positioned in the switch assembly to trap suspended magnetic particles in the oil that leaks past a pressure sensitive piston which actuates the switch. This prevents interference by the particles with the operation of the switch.

A still further object of the present invention is to provide a new and improved pressure sensitive switching mechanism of the type having a pressure responsive piston connected to move one of the switch members in which a resilient lost motion connection is provided therebetween to control the closing force applied to the switch.

Another object of the present invention is to provide a new and improved pressure sensitive switch which may be completely immersed in hydraulic fluid without adversely affecting the operation of the switching mechanism.

A more specific object of the present invention is to provide a new and improved pressure sensitive switch including a housing; a variable inductance coil assembly in the housing consisting of a generally annular coil fixed within the housing and a generally U-shaped permeable member extending through the coil and having axially extending leg members, the coil assembly being excited through suitable connectors by an AC power supply; with a pressure responsive means for varying the inductance of the coil assembly between a low impedance condition and a high impedance condition including another generally U-shaped magnetically permeable member defining an armature with its legs axially extending and defining with the U-shaped member in the coil assembly a variable air gap to vary the impedance of the coil assembly, said latter mentioned permeable member or armature being movable to a first position spaced from the coil assembly to establish a low impedance condition and a second position against the coil assembly to establish the high impedance condition, with a pressure responsive piston being provided slidably mounted in the housing and defining therein a chamber which is adapted to be connected to a hydraulic pressure source to sense the pressure of the source, means being provided connecting the piston to move the armature in lost motion fashion to assure the desired closing force on the armature when it is in the second position against the coil assembly; with a permanent magnet being provided for collecting foreign particles suspended in the fluid leaking from the fluid chamber; there being, also, provided a coil spring assembly for returning the armature to its first position spaced from the coil assembly against the force of hydraulic fluid in the fluid chamber.

Further objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal section of a pressure sensitive switch assembly incorporating the principles of the present invention; I

FIG. 2 is a longitudinal sectional view of the present pressure sensitive switch assembly taken on a plane rotated degrees from the view shown in FIG. 1;

FIG. 3 is a cross-sectional view taken generally along line 33 of FIG. 1 showing the armature assembly;

FIG. 4 is a cross-sectional view taken generally along line 44 of FIG. 2 illustrating a portion of the movable armature assembly, and;

FIG. 5 is a schematic usable with the mechanism.

illustration of a control circuit present I pressure sensitive switching While this invention is susceptible of embodiment in invention together with modifications thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

4 Referring now to the drawings and, particularly, FIGS. 1 and 2 thereof, the pressure sensitive switching mechanism of the present invention is seen to include a generally cylindrical main housing member 11, and an end closure 12 insertable within one end of the cylindrical housing 11. The switch 10 is insertable in a housing 13, only partially shown in FIG. 1, which defines a portion of the casing in a constant speed drive. The housing 13 has a stepped boss 14 which extends within the constant speed drive casing. The switch 10 is insertable within the housing 13 and boss 14 from outside the constant speed drive casing.

The pressure sensitive switch 10 also includes a coil assembly 16 fixed in housing member 11 and connected to a suitable source of AC supply through connectors 18, a movable armature assembly 19, and a pressure sensitive actuator 20 responsive to fluid pressure in a chamber 21 defined in the boss 14 to move the armature assembly 19 to either of its bistable positions to vary the impedance of the coil assembly 16, thereby providing either a low impedance or a high impedance condition in the coil assembly. It should be understood that chamber 21 is hydraulically connected to the hydraulic control within the constant speed drive housing so that fluid is delivered to the chamber 21.

When pressure above a predetermined value exists in hydraulic chamber 21 the pressure sensitive actuator mechanism moves to the left forcing the movable armature 19 to the left closing the air gap 22 and raising the impedance of the coil assembly 16 to a relatively high value. This high impedance condition through a suitable control circuit described in more detail below, provides an indication that the pressure in chamber 21 is above the predetermined value. On the other hand, when the pressure in chamber 21 falls below the predetermined value, the actuator assembly 20 will move to the right under the action of suitable biasing means which moves the armature assembly 19 away from the coil assembly producing a relatively large air gap 22 increasing the impedance in coil assembly 16 and thereby providing a second established condition in the control circuit which indicates that the pressure in chamber 21 is below the predetermined value.

Turning now to a more detailed discussion of the operating elements of the present pressure sensitive switching device, the housing member 11 is seen to include projecting ears 25 for use in mounting the switch assembly in the desired installation in the constant speed drive housing 13. The end closure 12 is generally cylindrical in construction and is adapted to be fitted within a central bore 27 in the main housing member 11. An insulator plug 28, fitted within a central opening in the closure 12, retains the electrical connectors 18 in position. Suitable leads electrically connect the connectors 18 with the coil assembly 16. The closure 12 has bifurcated projections 29 and 30, shown more clearly in FIG. 3, which extend to and about a stepped shoulder 32 in bore 27. The bifurcated projections 29 and 30 flank a magnetically permeable laminated core member 34 which is a part of the coil assembly 16, Closure 12 is retained within the housing member 11 by a suitable snap ring 36 which retains the projections 29 and 30 against shoulder 32. Suitable alignment pins 38 are provided for securing the alignment of the coil assembly 16 with respect to the armature assembly 19.

The coil assembly 16 is a variable inductance device adapted in a bistable fashion to achieve either a low impedance condition or a high impedance condition as noted above. It includes a generally annular c il and the generally U-shaped laminated magnetically permeable core member 34. The member 34 closely fits within a central opening in the coil 40 and has leg portions 42 and 43 which have ends 44 defining a portion of the air gap 22. As will be obvious to those skilled in the art, movement of the armature member 19 relative to the permeable member 34 varies the flux path to thereby vary the impedance of the coil assembly 16.

The armature assembly 19 includes a generally U-shaped permeable member 50 which may be constructed of laminated fenromagnetic plates similar to core member 34. A generally U-shaped retainer 52 surrounds and is fixed to the laminated core or armature 50. Included in the armature assembly 19 is a shaft or rod 54 extending through the retainer and the armature member 50. Rod 54 carries a permanent magnet ring 56. The armature 50, the carrier 52 a permanent magnet ring 56. The armature 50, the canrier 51 and the magnetic ring 56 are retained on the shaft or rod 54 by a flared portion 57 on the forward end of rod 54 which serves to urge the ring 56 against a suitable shoulder 58 on the shaft 54. The housing member 11 has a partition 60 in the central portion thereof with a generally rectangular slot 61 therein which slidably receives the retainer member 52,

The actuator assembly 20 is provided for moving the laminated core 50 from its position shown to FIGS. 1 and 2, which may be termed its first position, to a position abutting the laminated core 34, which may be termed its second position. The actuator assembly 20 includes a stepped generally cylindrical piston guide 65 seated within the right end of housing 11 and retained therein by a suit-able ring 67. A central bore 68 in the piston guide 65 slidably receives a piston member 70 which has an enlarged head 71 at one end thereof. In the rightmost position of the piston 70 the enlarged head 71 engages an annular projection 72 on the piston guide which serves as a stop for the piston.

The right end of piston 70 is subjected to the pressure of hydraulic fluid in chamber 21 and is thereby made responsive thereto. A closed end bore 75 is provided centrally in piston 70 for receiving the extending end of shaft or rod 54.

A suitable lost motion connection 76 is provided between the piston 70 and the armature assembly 19 to control the closing force applied to the armature assembly by the actuator 20. More specifically, this lost motion connection 76 includes a pin 77 fixed within diametral holes in the enlarged head 71 of piston 70, and extending through tan elongated slot 79 in the armature assembly shaft 54. A coiled compression spring 80 seated within piston bore 75 norm-ally urges the shaft 54 outwardly of the piston 70 to a position where pin 77 engages the right end of slot 79 as shown in FIG. 2, thus preventing any further extension of the shaft 54 from piston bore 75. As will appear hereinafter, the spring 80 is selected to provide the desired closing force between the movable armature 50 and the stationary core 34 irrespective of the force of hydraulic pressure acting on piston 70.

The actuator assembly, also, includes a coiled compression spring seated against a shoulder 91 in housing member 11 for urging the piston 70 to the right towards its retracted or first position. Spring 90 also bears against a generally cup shaped spring retainer 93 having a flange portion 94 providing a seat for one end of the compression spring 90. The retainer member 93 has a central opening 94a therein which freely receives the shaft 54. Thus, spring 90 urges the piston 70 to its retracted position through the retainer member 93. The spring 90 is selected with respect to the area of the fluid responsive side of the piston 70 so that at a predetermined pressure, e.g. psi. in chamber 21, the piston 70 will move to the left against the force of spring 90 closing the gap 22, and conversely when the pressure thereafter falls below the predetermined value, spring 90 will urge the piston 70 to the right opening the gap 22.

The retainer member 93 has projections 95 which flank the sides of the armature retainer 52 and are adapted to limit movement of the piston 70 to the left. More specifically, as piston 70 moves to the left carrying the retainer member 93, the projections 95 will abut the end of a coun terbore 97 in housing 11 thereby preventing any further movement of the piston 70. The limits of travel of the piston 70, defined by the shoulder formed by counterbore 97 and the stop 72 on the piston guide, are selected so that the piston 70 will move from its first position shown in FIGS. 1 and T2 to its second position where the spring seat projections 95 engage counterbore 97 a distance greater than necessary toachieve contact between the armature 50 and the core member 34. Thus, the piston over-travels the movement of the armature assembly 19.

Suitable drain passages 102 and 103 are provided in the housings 11 and 13 respectively for draining leakage fluid from the mechanism. It should be understood that fluid draining from passage 102 flows to a fluid reservoir within the constant speed drive housing 13. Ring seal 105 is provided for preventing the leakage of fluid from hydraulic chamber 21. To prevent the leakage of fluid from within the constant speed drive housing 13 between the pressure switch housing 11 and the inside of boss 14, another ring seal 106 is provided seated within a suitable annular recess in the periphery of housing 11.

The magnetic ring 56, referred to briefly above, is a permanent magnet designed to collect magnetic particles suspended in the hydraulic fluid that leaks past the piston 70 from hydraulic chamber 21. This prevents the foreign particles from collecting in the air gap 22 and interfering with the operation of the switch.

In operation, when the pressure in chamber 21 is below the predetermined level, the preloaded spring 90 maintains the piston 70 and the armature assembly 19 in the positon shown in FIGS. 1 and 2. The resulting large air gap 22 in the magnetic circuit causes the coil impedance to be low, and appreciable current flows through a load resistance R as shown in the control circuit of FIG. 5. A suitable indicating or control device 100 is provided across the load resistor R During this mode of operation the current 1;, is largely determined by the value of the load resistance R This condition may be selected as either the on or off condition as desired.

As the pressure in chamber 21 exceeds the predetermined level, the piston 70 will move to the left against the biasing force of compression spring 90. Before the projections 95 engage the counterbore 97 in housing 11, the armature core 50 will engage theends of the legs of core member 34 in the stationary coil assembly 16.thereby interrupting axial movement of the armature assembly 19. However, hydraulic pressure acting on the piston 70 continues to move the actuator assembly to the left until projections 95 engage counterbore 97. During this movement, the lost motion pin 77 will leave the right end of slot 79 in shaft 54 and assume a floating position therein. Thus, when armature 50 engages core member 34, the closing force therebetween is determined by the compression spring 80 acting against the rear end of armature assembly shaft 54 which may be selected as desired. The impedance of the coil assembly 16 then becomes high compared to the load resistance R since the air gap 22 is very small and the current I becomes very small as it is determined essentially by the reactance of the coil. The low current value flowing through load resistor R changes the bistable condition of the indicating or control device 100.

When the pressure in chamber 21 thereafter falls below the predetermined value, spring 90 will return the actuator member to the first retracted position permitting the return of armature assembly to the position shown in FIGS. 1 and 2.

One important feature of the present switching device is that the coil assembly 16 can be simple and rugged as it is not required to have a linear change of inductance with pressure. Instead, it is only necessary that the switch have a large inductance change between the open and closed positions.

Another important feature of the present invention is that no critical oil seals are required in the switch assembly and the whole mechanism can be run immersed in hydraulic fluid without the disadvantages attendant the operation of electrical contacts immersed in fluid.

I claim:

1. In a pressure switch, the combination comprising: electric switch means including first and second members relatively movable between a switch open position and a switch closed position; pressure responsive means for relatively moving said members between the switch open and the switch closed positions including a pressure responsive member movable to a first position in response to pressure below a predetermined value and movable to a second position in response to pressure above a prede termined value, means biasing said pressure responsive member to said first position, link means connecting said pressure responsive member to one of said switch members, means providing a yieldable lost motion connection in said link means, and resilient means biasing said one switch member away from said pressure responsive member whereby over-travel of said pressure responsive member will not significantly vary the closing force on the switch members.

2. In a pressure switch, the combination comprising: electric switch means including first and second members relatively movable between a switch open position and a switch closed position; pressure responsive means for relatively moving said members between the switch open and the switch closed positions including a pressure responsive piston movable to a first position in response to pressure below a predetermined value and movable to a second position in response to pressure above a predetermined value, means for limiting movement of said piston beyond said second position, means biasing said piston to the first position, link means connecting said pressure responsive member to one of said switch members, means providing a yieldable lost motion connection in said link means, and resilient means biasing said one switch member away from said pressure responsive member, said piston being movable between said first and second positions a distance greater than necessary to move the switch members between the open and closed positions, whereby over-travel of said pressure responsive member will not significantly vary the closing force on the switch members.

3. In a pressure switch the combination comprising: variable inductance means adapted to control an external device, means for varying the inductance of said inductance means including a permeable member movable relative to said variable inductance means between a first position wherein the impedance of said variable inductance means is low and a second position wherein the impedance of said variable inductance means is high, and pressure responsive means for moving said permeable member between said first and second positions, including a pressure responsive member movable to a first position in response to pressure below a predetermined value and movable to a second position in response to pressure above a predetermined value, means biasing said pressure responsive member to said first position, link means connecting said pressure responsive member to said permeable member, means providing a yieldable lost motion connection in said link means, and resilient means biasing said permeable member away from said pressure responsive member whereby over-travel of said pressure responsive member will not significantly vary the closing force on the variable inductance means.

4. In a pressure switch the combination comprising: variable inductance means adapted to control an external device, means for varying the inductance of said inductance means including a permeable member movable relative to said variable inductance means between a first position wherein the impedance of said variable inductance means is low and a second position wherein the impedance of said variable inductance means is high, and pressure responsive means for moving said permeable member between said first and second positions, a pressure responsive piston movable to a first position in response to pressure below a predetermined value and movable to a second position in response to pressure above a predetermined value, means for limiting movement of said piston beyond said second position, means biasing said piston to the first position, link means connecting said pressure responsive member to said permeable member, means providing a yieldable lost motion connection in said link means, and resilient means biasing said permeable member away from said pressure responsive member, said piston being movable between said first and second positions a distance greater than necessary to move said permeable member between the open and closed positions, whereby over-travel of said pressure responsive member will not significantly vary the closing force on the switch members.

5. A pressure switch, comprising: a variable inductance coil assembly, means for supplying a varying signal to said coil assembly; and pressure responsive means for varying the inductance of said coil assembly between a low impedance condition and a high impedance condition, said coil assembly including a first permeable core member, a second permeable core member, coil means associated with said second permeable core member, said first and second permeable core members when together defining a high impedance condition and when spaced defining a relatively low impedance condition, said second core member being constructed so that when said first core member is in said first position a low impedance condition is established, said first permeable core member being movable to a first position spaced from said second permeable core member to establish said low impedance condition and being movable to a second position closer to said second permeable core member to establish said high impedance condition, means defining a fluid chamber, a pressure responsive piston slidably mounted in said fluid chamber, means connecting said piston to move said permeable member, spring means urging said piston to a first position whereat the permeable member is in one of said positions, said fluid chamber being constructed so that fluid therein above a predetermined pressure values the piston to a second position against the biasing force of said spring means whereat the permeable member is moved to the other position.

6. A pressure switch as defined in claim 5, wherein said means connecting said piston to move said permeable member includes link means having a lost motion connection, means biasing said permeable member away from said piston, the distance between the first and second positions of the piston being greater than that necessary to move said permeable member between its first and second positions whereby the biasing means between the piston and the permeable member determine the force on the permeable member urging it toward the coil assembly when the permeable member is in said second position.

7. A pressure switch as defined in claim and further including means for collecting foreign particles suspended in the fluid leaking from the fluid chamber.

8. A pressure switch as defined in claim 7 wherein said collecting means includes a permanent magnet in said housing adjacent said piston and between the piston and the coil assembly whereby foreign particles are prevented from contaminating the air gap between the coil assembly and the permeable member.

9. A pressure switch a defined in claim 7, wherein said coil assembly includes a generally annular coil fixed within said housing, and a generally U-shaped permeable member extending through said coil and having axially extending leg members, the ends of said leg members extending beyond said coil and defining with the permeable member in air gap.

10. A pressure switch as defined in claim 9, wherein said first permeable member is a generally U-shaped armature with its legs axially extending and having ends adjacent the ends of the coil assembly permeable member, said housing having axially extending recess means for receiving said first permeable member.

11. In a pressure switch the combination comprising: variable inductance means adapted to control an external device, means for varying the inductance of said inductance means including a first permeable core member, a second permeable core member, coil means associated with said second permeable core member, said first and second permeable core members when together defining a high impedance condition and when spaced defining a relatively low impedance condition, said second core member being constructed so that when said first core member is in said first position a low impedance condition is established, said first core member being movable relative to said variable inductance means between a first position spaced from said second core member wherein the impedance of said variable inductance means is low and a second position closer to said second core member wherein the impedance of said variable inductance means is high, pressure responsive means for moving said permeable member between said first and second positions, and means for collecting foreign particles to prevent the collection of such particles in the air gap between the variable inductance means and said permeable member.

12. A pressure switch as defined in claim 11, wherein said collecting means includes a permanent magnet separate from and adjacent said core member.

13. In a pressure switch the combination comprising: variable inductance means adapted to control an external device, means for varying the inductance of said inductance means including a permeable member movable relative to said variable inductance means between a first position wherein the impedance of said variable inductance means is low and a second position wherein the impedance of said variable inductance means is high, and pressure responsive means for moving said permeable member between said first and second positions, including a pressure responsive member movable to a first position in response to pressure below a predetermined value and movable to a second position in response to pressure above a predetermined value, means biasing said pressure responsive member to said first position, link means connecting said pressure responsive member to said permeable member, means providing a yieldable lost motion connection in said link means, and resilient means biasing said permeable member away from said pressure responsive member whereby over-travel of said pressure responsive member will not significantly vary the closing force on the variable inductance means, and means for collecting foreign particles to prevent the collection of such particles in the air gap between the variable inductance means and said permeable member, said collecting means including a permanent magnet adjacent said permeable member.

14. A pressure switch, comprising: a housing; a variable inductance coil assembly in said housing, means for supplying a varying signal to said coil assembly; and pressure responsive means for varying the inductance of said coil assembly between a low impedance condition and a high impedance condition including a permeable member in said housing adjacent said coil assembly, said permeable member being movable to a first position spaced from said coil assembly to establish said low impedance condition and being movable to a second position closer to said coil assembly to establish said high impedance condition, a pressure responsive piston slidably mounted in said housing and defining therein a fluid chamber, means connecting said piston to move said permeable member, spring means urging said piston to a first position whereat the permeable member is in said first position, said fluid chamher being constructed so that fluid therein above a predetermined pressure value moves the piston to a second position against the biasing force of said spring means whereat the permeable member is in said second position, means for collecting foreign particles suspended in the fluid leaking from the fluid chamber, said coil assembly including a generally annular coil fixed within said housing, and a generally U-shaped permeable member extending through said coil and having axially extending leg members, the ends of said leg members extending beyond said coil and defining with the permeable member an air gap, said first permeable member being a generally U-shaped armature with its legs axially extending and having ends adjacent the ends of the coil assembly permeable member, said housing having axially extending recess means for receiving said first permeable member, said piston having an enlarged head portion, shoulder means in said housing engageable with said head means in the first position of said piston, said piston having an axial bore therein, said link means including a rod fixed to said first permeable member and slidable in said bore, said biasing means between the piston and the first permeable member including a compression spring in said bore and urging said rod from said bore, said lost motion connection including an elongated slot and pin connection between said piston and said rod.

15. A pressure switch, comprising: a housing; a variable inductance coil assembly in said housing, means for supplying :a varying signal to said coil assembly; and pressure responsive means for varying the inductance of said coil assembly between a low impedance condition and a high impedance condition including a permeable member in said housing adjacent said coil assembly, said permeable member being movable to a first position spaced from said coil assembly to establish said low impedance condition and being movable to a second position closer to said coil assembly to establish said high impedance condition, a pressure responsive piston slidably mounted in said housing and defining therein a fluid chamber, means connecting said piston to move said permeable member, spring means urging said piston to a first permeable member including a compression spring in said bore and urging said rod from said bore, said lost motion connection including an elongated slot and pin connection between said piston and said rod, a spring seat member engaging the enlarged end of the piston, said spring means urging said piston to its first position including a coil spring seated within said housing and engaging said spring seat member, said spring seat member having bifurcated projections adapted to stop said piston in the second position which extend axially and flank the first permeable member.

16. A pressure switch, comprising: a housing; a variable inductance coil assembly in said housing, means for supplying a varying signal to said coil assembly; and pressure responsive means for varying the inductance of said coil assembly between a low impedance condition and a high impedance condition including a permeable member in said housing adjacent said coil assembly, said permeable ,member being movable to a first position spaced from said coil assembly to establish said low impedance condition and being movable to a second position closer to said coil assembly to establish said high impedance condition, a pressure responsive piston slidably mounted in said housing and defining therein a fluid chamber, means connecting said piston to move said permeable member, spring means urging said piston to a first position whereat the permeable member is in said first position, said fluid chamber being constructed so that fluid therein above a predetermined pressure value moves the piston to a second position against the biasing force fixed within said housing,

first position whereat the permeable member is in said first position, said fluid chamber being constructed so that fluid therein above a predetermined pressure valve moves the piston to a second position against the biasing force of said spring means whereat the permeable member is in said second position, means for collecting foreign particles suspended in the fluid leaking from the fluid chamber, said coil assembly including a generally annular coil fixed within said housing, and a generally U-sh-aped permeable member extending through said coil and having axially extending leg members, the ends of said leg members extending beyond said coil and defining with the permeable member an air gap, said first permeable member being a generally U-shaped armature with its legs axially extending and having ends adjacent the ends of the coil assembly permeable member, said housing having axially extending recess means for receiving said first permeable member, said piston having an enlarged head portion, shoulder means in said housing engageable with said head means in the first position of said piston, said piston having an axial bore therein, said link means including a rod fixed to said first permeable member and slidable in said bore, said biasing means between the piston and the of said spring means whereat the permeable member is in said second position, means for collecting foreign particles suspended in the fluid leaking from the fluid chamber, said coil assembly including a generally annular coil and a generally U-shaped permeable member extending through said coil and having axially extending leg members, the ends of said leg members extending beyond said coil and defining with the permeable member an air gap, said first permeable member being a generally U-shaped armature with its legs axially extending and having ends adjacent the ends of the coil assembly permeable member, said housing having axially extending recess means for receiving said first permeable member, said piston having an enlarged head portion, shoulder means in said housing engageable with said head means in the first position of said piston, said piston having an axial bore therein, said link means including a rod fixed to said first permeable member and slidable in said bore, said biasing means between the piston and the first permeable member including a compression spring in said bore and urging said rod from said bore, said lost motion connection including an elongated slot and pin connection between said piston and said rod, and further including a permanent magnet mounted on the extending portion of said rod for collecting foreign particles in the fluid leaking from the fluid chamber.

References Cited UNITED STATES PATENTS 2,487,083 11/1949 Warshaw 336134 X 2,913,688 11/1959 Slebodnik et al. 336134 X 2,930,009 3/1960 Cogley et al 336l34 X BERNARD A. GILHEANY, Primary Examiner. H. BROOME, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,350 ,523 c r 31 1967 Evans W. Erikson It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, line 4, a

corporation of Illinois" should read a corporation of Delaware Column 7, lines 33 to 36, cancel "said second core member being constructed so that when said first core member is in said first position a low impedance condition is established,"; line 41, after "condition," insert said second core member being constructed so that when said first core member is in said first position a low impedance condition is established, Column 7, line 48, "values" should read value moves Column 8, line 4, "in" should read an Signed and sealed 16th day of December 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

1. IN A PRESSURE SWITCH, THE COMBINATION COMPRISING: ELECTRIC SWITCH MEANS INCLUDING FIRST AND SECOND MEMBERS RELATIVELY MOVABLE BETWEEN A SWITCH OPEN POSITION AND A SWITCH CLOSED POSITION; PRESSURE RESPONSIVE MEANS FOR RELATIVELY MOVING SAID MEMBERS BETWEEN THE SWITCH OPEN AND THE SWITCH CLOSED POSITIONS INCLUDING A PRESSURE RESPONSIVE MEMBER MOVABLE TO A FIRST POSITION IN RESPONSE TO PRESSURE BELOW A PREDETERMINED VALUE AND MOVABLE TO A SECOND POSITION IN RESPONSE TO PRESSURE ABOVE A PREDETERMINED VALUE, MEANS BIASING SAID PRESSURE RESPONSIVE MEMBER TO SAID FIRST POSITION, LINK MEANS CONNECTING SAID PRESSURE RESPONSIVE MEMBER TO ONE OF SAID SWITCH MEMBERS, MEANS PROVIDING A YIELDABLE LOST MOTION CONNECTION IN SAID LINK MEANS, AND RESILIENT MEANS BIASING SAID ONE SWITCH MEMBER AWAY FROM SAID PRESSURE RESPONSIVE MEMBER WHEREBY OVER-TRAVEL OF SAID PRESSURE RESPONSIVE MEMBER WILL NOT SIGNIFICANTLY VARY THE CLOSING FORCE ON THE SWITCH MEMBERS. 